1. Description of Related Art
The present invention refers to the collection of the yarn produced or processed by textile machines to be wound onto reels. In industrial practice, the technique generally adopted is that of collecting the yarns by rotating a tube, carried idle by the spindles of a reel-carrying arm and taking up the yarn arriving from a feeding organ to wind it onto itself. The reel is thus formed by pulling and winding the yarn onto its surface, being rotated in turn with a driving roller underneath; the reel rests on this and winds the yarn at a substantially constant linear speed, irrespective of the dimensions assumed by the reel as winding proceeds, and depending only on the rotating speed of said driving roller. The yarn is thus wound in spirals onto the rotating reel and distributed with a backward and forward movement on its surface by a thread-guiding device.
For most of the subsequent uses of the yarn wound onto the reel in downstream processes, it is necessary for the reel to be conically shaped, this is typical when it is required to unwind the yarn axially from the fixed reel, placed on creels or similar supports.
2. Field of the Invention
The present invention refers more particularly to the downstream winding onto conical reels of the yarns produced, processed, fed or in any way obtained from textile machines located upstream at a constant speed.
A typical example of these textile machines which produce yarn at a constant linear speed is represented by rotor spinning machines, currently known as open-end spinning machines, while in the formation of the conical reel the collecting speed has a pulsating trend.
To illustrate thoroughly the questions involved with conical reels and the technical solutions proposed with the present invention, reference is therefore made, in the following description, to the collection of open-end yarns on conical reels, as an example without limitation.
The cause of the collection speed pulsation on a conical reel derives essentially from two circumstances. The first circumstance is the swinging distribution of the yarn on the reel being formed with a thread-guiding device ranging between the two winding ends. This range periodically lengthens and shortens the length of the section of swinging thread, from the last transverse restraint to the thread guide. It is minimum when the thread guide deposits the thread on the central part of the reel and the guide is at the half-way stage of its stroke, and it is maximum when the thread guide deposits the thread at the two bases of the reel and it is at the ends of its stroke. This periodic variation of the length of the thread path is therefore translated into a first pulsation of the thread take-up speed: at each moment it would be necessary to bring up from the bottom a length of thread corresponding to the length of thread wound onto the reel increased or decreased by the periodic variation of lengthxe2x80x94positive and negativexe2x80x94of the path which joins the organ supplying the thread at constant speed and the collecting organ at pulsating speed.
This first circumstance is shared with the procedure for winding onto straight cylindrical reels. The second circumstance, on the other hand, derives from the conical shape of the reel. Even though the mean collecting speed is kept the same as the speed at which the thread arrives from the open-end spinning machine, a second speed pulsation is encountered. Generally the semi-conical formation (or tilting) of the tubes is not very accentuated, being kept usually below 5xc2x0, but, at the present reel winding speeds, the consequent pulsations of the take-up speed are not at all negligible.
When the thread is wound onto the part with the largest diameterxe2x80x94currently at the bottom of the reelxe2x80x94it is picked up at a greater speed, higher than the speed at which the thread arrives at constant speed from the supplying spinning machine, and so it is subjected to greater tension; instead, when the thread is wound onto the part with a smaller diameterxe2x80x94currently at the top of the reelxe2x80x94the inverse situation occurs, the thread is loose because it is picked up at a lower speed, less than the constant speed of the thread arriving from the spinning machine.
The technical problem which is essentially presented for collecting yarn with winding on conical reels derives from the sum of the pulsations of the thread take-up speed and from the tensions which this produces in the thread in the absence of effective remedies. In addition to the periodic pulsation of the thread take-up due to the variation of the transverse coordinate of the instantaneous point of winding, there is the periodic speed pulsation due to the more or less accentuated conical shape of the reel being formed. The trend of the sum of the two pulsations with reference to the transverse coordinate of the traversing path is not linear, but presents a trend with a positive and increasing derivative in the direction of the greater diameter of the reel being wound. This trend is schematically illustrated in FIG. 1. In short, the basic problem lies in having to combine a system for the production of yarn supplied intrinsically at a constantly linear speed with a collecting system which instead collects it intrinsically at a pulsating linear speed with considerable frequency around a mean value which corresponds to the speed of delivery. There must also be considered the necessity that the tension of the winding thread must be very precisely regulated throughout the duration of winding, depending on the density and on the consistency required for the subsequent use of the reel; for high quality reels the precision required is reckoned in gram/weight.
In the prior art numerous technical solutions have been proposed for the problems connected with this type of winding. During reel rotation, drive rollers are generally used which have an annular strip with a greater friction coefficient to determine the drive point on the generatrix of the conical reel and therefore the transmission ratio between roller and conical reel.
U.S. Pat. Nos. 4,002,306 and 4,113,193 teach how to insert in the path of the thread being collected a line of deviating elements, which may be alternatively spaced from one another transversely by the action of springs under tension, which cause the thread to have a movement that is all the more tortuous, the lower the tension of the thread. This system allows the creation of a reserve length of thread when it is not very tight and to return it when the thread tension returns. In U.S. Pat. Nos. 4,133,493 and 4,312,482 a similar system is proposed for creating a path with variable tortuousity depending on the thread tension.
These technical solutions require relatively high yarn tensions in order to follow the frequency of the pulsations during winding, and they involve a complex mechanical control. They do not allow the production of soft reels and they require limitation of the yarn take-up speed, due to the quite appreciable masses in alternative motion.
Technical solutions have also been proposed that are based on the variation of the transmission ratio between the drive roller and the driven reel, shifting the drive point on the generatrix of the conical reel alternately towards the bottom and the top of the conical reel, depending on the tension values found in the yarn being picked up, for example as described in patent EP 285.204 in the name of the same applicant. The devices of the prior art are complicated, expensive and their applications are limited.
The aim of the present invention is to realise a device for collecting, on conical reels, yarns produced or supplied at a constant linear speed by textile machines located upstream, which overcomes the inconveniences of the devices of the prior art.
The device according to the invention is defined, in its essential components, in the first claim, while its variants and preferential embodiments are specified and defined in the dependant claims.